This research program is concerned with the retina and optic ganglia of arthropods as a useful experimental system in which general problems of photoreception and sensory information processing can be attacked at several levels. The techniques include: microspectrophotometry of visual pigments and their photoproducts, intra- and extra-cellular recording of receptor and synaptic potentials, and analysis of spike discharge of visual interneurons; fine-structural analysis of isolated rhabdoms.